ATM inverse multiplexing system

Abstract

A method of reducing error-multiplication due to error events in a cell stream transmitted as a plurality of cell sub-streams which includes the steps of receiving an incoming cell stream in the form of an ordered sequence of cells including payload cells, transmitting the incoming cell stream in a round robin fashion on a plurality of physical links such that the ordered sequence of cells is transmitted as a plurality of cell sub-streams, with each cell sub-stream having a multiplexed set of cells from the incoming cell stream, and inserting stuff (st) cells into the cell sub-streams so as to form continuous streams of data. Sequence number cells which are inserted periodically into each cell sub-stream, are used to align the cell sub-streams in frames. Sets of cell location information for the cell sub-streams are encoded and contain the location of payload cells and st cells located within a corresponding cell sub-stream. The sets of cell location information are passed on to a receiving end where they are re-constructed at the receiving end. A sequence of the ordered sequence of cells from the cell sub-streams is re-constructed including decoding the sets of cell location information to identify and locate errored cells and missing cells within the cell sub-streams and demultiplexing and releasing error-free payload cells from the cell sub-streams.

What is claimed is:  
     
       1. A method of reducing error-multiplication due to error events in a cell stream transmitted as a plurality of cell sub-streams in an inverse multiplexing system whose actions include: 
       receiving an incoming cell stream comprising an ordered sequence of cells including payload cells;  
       transmitting the incoming cell stream in a round robin fashion on a plurality of physical links such that the ordered sequence of cells is transmitted as a plurality of cell sub-streams, each cell sub-stream comprising a multiplexed set of cells from said incoming cell stream;  
       inserting stuff (st) cells into said cell sub-streams so as to form continuous streams of data;  
       inserting sequence number (S) cells periodically into each cell sub-stream, wherein said S cells are used to align said cell sub-streams in frames; and  
       re-constructing at the receiving end a sequence of said ordered sequence of cells from said cell sub-streams,  
       the method comprising the steps of:  
       encoding sets of cell location information for the cell sub-streams, each of said sets of cell location information comprising the location of payload cells and st cells located within a corresponding cell sub-stream;  
       passing said sets of cell location information to a receiving end; and  
       decoding the sets of cell location information to identify and locate errored cells and missing cells within the cell sub-streams and demultiplexing and releasing error-free payload cells from the cell sub-streams.  
     
     
       2. A method according to  claim 1 , wherein said sets of cell location information are encoded into transmitted framing cells inserted in said cell sub-streams. 
     
     
       3. A method according to  claim 2 , wherein said transmitted framing cells are transmitted after transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       4. A method according to  claim 2 , wherein said transmitted framing cells are transmitted before transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       5. A method according to  claim 2 , wherein said transmitted framing cells are transmitted before and after transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       6. A method according to  claim 2 , wherein said pre-selected cells are selected from at least one of: (a) said S cells and (b) said st cells. 
     
     
       7. A method according to  claim 6 , wherein said st cells are inserted into said cell sub-streams during intervals when idle cells would otherwise be inserted into said cell sub-streams for cell rate decoupling. 
     
     
       8. A method according to  claim 7 , including marking errored cells within said cell sub-streams. 
     
     
       9. A method according to  claim 8 , wherein said re-constructing step includes distinguishing between header errors and payload errors in said pre-selected cells so that cell location information stored in an errored pre-selected cell having an error-free payload may continue to be used to reconstruct the sequence of said ordered sequence of cells. 
     
     
       10. A method according to  claim 2 , wherein said re-constructing step includes distinguishing between header errors and payload errors in said pre-selected cells so that cell location information stored in an errored pre-selected cell having an error-free payload may continue to be used to reconstruct the sequence of said ordered sequence of cells. 
     
     
       11. A method according to  claim 10 , wherein said pre-selected cells are transmitted after transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       12. A method according to  claim 10 , wherein said pre-selected cells are transmitted before transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       13. A method according to  claim 2 , wherein said pre-selected cells contain sets of cell location information for both cell sub-streams transmitted before said pre-selected cells and cell sub-streams transmitted after said pre-selected cells. 
     
     
       14. A method according to  claim 2 , wherein said re-constructing step includes storing cells from said cell sub-streams in a buffer. 
     
     
       15. A method according to  claim 14 , wherein said re-constructing step includes releasing cells stored in said buffer at a rate sufficient to maintain a predetermined number of stored cells within said buffer. 
     
     
       16. A method according to  claim 15 , wherein said re-constructing step includes flushing all cells aligned in the same frame for all cell sub-streams upon failure to identify an unknown cell within at least one such frame. 
     
     
       17. A method according to  claim 1 , wherein said sets of cell location information are inserted in framing cells for transmission to said receiving end. 
     
     
       18. A method according to  claim 1 , wherein said sets of cell location information are inserted in to available space within transmitted st cells. 
     
     
       19. A method according to  claim 1 , wherein said st cells are inserted into said cell sub-streams during intervals when idle cells would otherwise be inserted into said cell sub-streams for cell rate decoupling. 
     
     
       20. A method according to  claim 1 , wherein errored cells in said incoming cell stream are replaced with pre-selected cells for transmission in said cell sub-streams. 
     
     
       21. A method according to  claim 1 , including marking errored cells within said cell sub-streams. 
     
     
       22. A method according to  claim 21 , wherein said errored cells are marked as errored using available space within said errored cells. 
     
     
       23. A method according to  claim 1 , including distinguishing between an error in a header and an error in a payload of a transmitted framing cell so that cell location information stored in an errored framing cell with an error-free payload may continue to be used to re-construct the sequence of said ordered sequence of cells. 
     
     
       24. A method according to  claim 1 , where said framing cells all have identical format and fields for location information. 
     
     
       25. A method according to  claim 1 , wherein said framing cells all contain stuff location and latest status information. 
     
     
       26. A method according to  claim 1 , wherein said framing cells have a status and control change indication field that is incremented only when there is a change in any status information field which allows a receiver implementation to quickly determine if the status fields in the framing cells have changed since the last one received over the same link. 
     
     
       27. A method according to  claim 1 , wherein said sets of cell location information are inserted into framing cells at least one frame before frames for ones of said cell sub-streams corresponding to said sets of cell location information. 
     
     
       28. A method according to  claim 1 , wherein said sets of cell location information are inserted in to framing cells at least one frame after frames for ones of said cell sub-streams corresponding to said sets of cell location information. 
     
     
       29. A method according to  claim 1 , wherein said sets of cell location information are inserted only into corresponding ones of said cell sub-streams. 
     
     
       30. A method according to  claim 1 , wherein cell location information is stored in a transmitted framing cell so as to overlap with cell location information stored in another transmitted framing cell. 
     
     
       31. A method according to  claim 30 , wherein errored cells in said incoming cell stream are replaced with st cells for transmission in said cell sub-streams. 
     
     
       32. A method according to  claim 1 , including transmitting redundant cell location information over more than one of said physical links. 
     
     
       33. A cell-based system for reducing error-multiplication due to error events in a cell stream transmitted as a plurality of cell sub-streams, the system comprising: 
       (a) a first assembly coupled to a plurality of links and an incoming cell stream comprising an ordered sequence of cells including payload cells;  
       (b) a second assembly coupled to the plurality of links;  
       wherein said first assembly comprises:  
       means for encoding and transmitting sets of cell location information for said cell sub-streams, each of said sets of cell location information comprising the location of payload cells and framing cells located within a corresponding cell sub-stream;  
       and wherein said second assembly comprises:  
       means for receiving said sets of cell location information; and  
       means for re-constructing a sequence of said ordered sequence of cells from said cell sub-streams robustly, by means for decoding said sets of cell location information to identify and locate errored cells and missing cells within said cell sub-streams and means for demultiplexing and releasing error-free payload cells from the cell sub-streams.  
     
     
       34. A system according to  claim 33 , wherein said first assembly includes means for inserting said sets of cell location information into pre-selected cells inserted in said cell sub-streams. 
     
     
       35. A system according to  claim 34 , wherein said pre-selected cells are selected from at least one of: (a) said S cells and (b) said st cells. 
     
     
       36. A system according to  claim 35 , wherein said means for inserting st cells includes means for inserting said st cells into said cell sub-streams during intervals when idle cells would otherwise be inserted into said cell sub-streams for cell rate decoupling. 
     
     
       37. A system according to  claim 36 , wherein said first assembly includes means for storing cell location information in a transmitted framing cell so as to overlap with cell location information stored in another transmitted framing cell. 
     
     
       38. A system according to  claim 34 , wherein said second assembly includes means for distinguishing between header errors and payload errors in said pre-selected cells so that cell location information stored in an errored pre-selected cell having an error-free payload may continue to be used to reconstruct the sequence of said ordered sequence of cells. 
     
     
       39. A system according to  claim 35 , wherein said second assembly includes means for distinguishing between header errors and payload errors in said pre-selected cells so that cell location information stored in an errored pre-selected cell having an error-free payload may continue to be used to reconstruct the sequence of said ordered sequence of cells. 
     
     
       40. A system according to  claim 39 , wherein said means for transmitting the incoming cell stream in a round robin fashion on the links includes means for transmitting said pre-selected cells after transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       41. A system according to  claim 39 , wherein said means for transmitting the incoming cell stream in a round robin fashion on the links includes means for transmitting said pre-selected cells before transmitting cell sub-streams corresponding to said sets of cell location information. 
     
     
       42. A system according to  claim 34 , wherein said first assembly includes means for inserting into said pre-selected cells sets of cell location information for both cell sub-streams transmitted before said pre-selected cells and cell sub-streams transmitted after said pre-selected cells. 
     
     
       43. A system according to  claim 34 , wherein said second assembly includes means for storing cells from said cell sub-streams in a plurality of buffers. 
     
     
       44. A system according to  claim 43 , wherein said re-constructing means includes means for releasing cells stored in said buffers at a rate sufficient to maintain a predetermined number of stored cells within said buffers. 
     
     
       45. A system according to  claim 44 , wherein said second assembly includes means for flushing from said buffers all cells aligned in the same frame for all cell sub-streams upon failure to identify an unknown cell within at least one such frame. 
     
     
       46. A system according to  claim 44 , wherein said plurality of buffers are circular buffers. 
     
     
       47. A system according to  claim 46 , wherein, for each circular buffer, said second assembly includes: 
       (i) a write pointer which is incremented upon storage of an incoming cell into a corresponding buffer;  
       (ii) a read pointer which is incremented each time a cell is released from the corresponding buffer;  
       (iii) a total cells counter which is incremented each time the write pointer is incremented for the corresponding buffer and decremented each time the read pointer is incremented for the corresponding buffer; and  
       (iv) a payload cell counter which is incremented each time a payload cell is stored in the circular buffer and decremented each time a payload cell is released from the corresponding buffer.  
     
     
       48. A system according to  claim 33 , wherein said first assembly includes means for inserting said sets of cell location information into framing cells at least one frame before frames for ones of said cell sub-streams corresponding to said sets of cell location information. 
     
     
       49. A system according to  claim 33 , wherein said first assembly includes means for inserting said sets of cell location information into framing cells at least one frame after frames for ones of said cell sub-streams corresponding to said sets of cell location information. 
     
     
       50. A system according to  claim 33 , wherein said first assembly includes means for inserting said sets of cell location information only into corresponding ones of said cell sub-streams. 
     
     
       51. A system according to  claim 33 , wherein said first assembly is couplable to a first asynchronous transfer mode (ATM) layer device and a plurality of first physical layer devices coupled to said physical links, and wherein said second assembly is couplable to a second ATM layer device and a plurality of second physical layer devices coupled to said physical links. 
     
     
       52. An apparatus for robustly re-combining a plurality of distributed cell sub-streams into a sequenced cell stream, the apparatus comprising: 
       means for receiving sets of cell location information corresponding to transmitted cell sub-streams; and  
       means for robustly re-constructing an ordered sequence of  
       cells from said transmitted cell sub-streams including means for decoding said sets of cell location information to identify and locate errored cells and missing cells within said transmitted cell sub-streams and means for demultiplexing and releasing error-free payload cells from said transmitted cell sub-streams.  
     
     
       53. A method of robustly re-combining a plurality of distributed cell sub-streams into a sequenced cell stream, the method comprising the steps of: 
       receiving sets of cell location information corresponding to transmitted cell sub-streams; and  
       robustly re-constructing an ordered sequence of cells from said transmitted cell sub-streams by decoding said sets of cell location information to identify and locate errored cells and missing cells within said transmitted cell sub-streams and demultiplexing and releasing error-free payload cells from said transmitted cell sub-streams.